Fastener protrusion sensor

ABSTRACT

The present invention relates to a protrusion sensor that determines the acceptability of a rivet within a component. The sensor includes a baseline detector which remains stationary, a movable detector which moves with a bucking bar module and produces a first signal proportionate to a distance between the baseline detector and the movable detector, and a CPU electronically connected to the movable detector and receiving the first signal. The CPU determines whether the rivet is acceptable by inputting a first distance when the bucking bar module is clamping an inside surface of the component, inputting a second distance when the bucking bar module is seated against a shank of the rivet, subtracting the second distance from the first distance to determine a length of the shank protruding from the inside surface of the component, and comparing the length of the shank against an internal table of rivet lengths to determine whether the proper rivet was loaded into the component or whether the rivet is within an acceptable tolerance.

This Appln claims the benefit of U.S. Provisional Appln Ser. No.60/066,614 filed Nov. 26, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for measuring a fastener, andmore particularly, to a device for measuring the shank of a fastener.

2. Background of the Invention

Traditional manufacturing techniques for assembling components toproduce large mechanical structures to a specified contour have reliedon fixtured tooling techniques utilizing assembly jigs and templates tolocate the parts correctly relative to one another. Unfortunately, thismethod often yielded parts outside of acceptable tolerance because ofimperfections in the templates or changes in the fixtured tooling causedby temperature variations.

To solve the problems encountered by traditional techniques, a systemand method for assembling components was developed that utilized spatialrelationships between key features of subassemblies as represented bycoordination holes drilled into the subassemblies using numerical partdefinition records. The subassemblies were made intrinsicallydeterminate of the dimensions and contour of the assembly.

The use of key features to determine the dimensions and contour of anairplane fuselage section is shown in FIG. 1. Here, a skin 20 has aplurality of stringers 22 and a plurality of shear ties 24 rivetedthereon. A frame member 30 having a curved contour which is the same asthe desired contour of the airplane fuselage is then riveted to theshear ties 24 and stringer clips 26.

The stringers 22, the shear ties 24 and the stringer clips 26 must befastened to the fuselage skin 20 with extreme accuracy and consistency.Accuracy of parts manufacture ensures that the airplane will cometogether perfectly with no pre-stressed parts and no cosmeticimperfections.

Initially, a computer numerically controlled (CNC) machine tool performsmachining operations on the skin 20. Coordination holes are drilled inthe skin 20 and the stringers 22. Corresponding coordination holes arealso drilled in the shear ties 24 and the stringer clips 26. A finalmachining operation of edge routing is performed by a high speed routingend-effector to route the edges of the fuselage skin 20 to the correctdimensions, as specified by the original part definition data base, byaccurately locating the edges of the skin relative to the coordinationholes in the skin.

The stringers 22 are tack fastened to the skin 20 through their alignedcoordination holes. Then the shear ties 24 and stringers 22 are drilledand riveted to the skin 20. The stringer clips 26 are inserted at thecorrect location and are held in place while drilled and riveted to forma panel 34.

The skin 20 also has a series of panel-to-panel coordination holes 32drilled along the edge of the skin 20. The panel-to-panel coordinationholes 32 are used to position the panels 34 relative to each other. Thepanels 34 are still relatively flexible so the ultimate configuration isdetermined by the parts and their matched coordination holes.

The panel-to-panel coordination holes 32 are aligned on adjacent holesand sealant is applied between the facing surfaces of the panel edges.The panels 34 are aligned so that the panel-to-panel coordination holes32 on adjacent panels 34 line up exactly and the two panels are fastenedtogether at their adjacent edges by temporary deco fasteners through thecoordination holes. The panels are then drilled and riveted topermanently fasten them together to form a super panel 36.

Coordination holes are drilled into the frames 30 and are aligned withthe coordination holes in the stringer clips 26. The frames 30 arefastened and their alignment determines the contour of the super panel36. Thus, the contour is independent of any hard tooling. Once the superpanel 36 is formed, the temporary cleco fasteners holding the parts inposition are replaced by permanent fasteners.

The super panels 36 are temporarily fastened using the panel-to-panelcoordination holes 32 to form fuselage quarter panels which are in turntemporarily fastened to form a lower fuselage lobe 38A and an upperfuselage lobe 38B, as shown in FIGS. 2A and 2B. A floor grid 40 isaligned with the lower lobe 38A using coordination holes, and isfastened in place. The fixture 44 does not determine the contour ordimensions of the fuselage. Instead, the coordination holes drilled intothe floor grid 40 determines the cross-dimensions of the fuselage 42.

Once the frame members 30 and lobe skin coordination holes 46 are allaligned and temporarily fastened with deco fasteners, they are drilledto form the final fuselage section 42, as shown in FIG. 2B. The fuselagesection 42 is then disassembled, de-burred, cleaned, and sealant isadded.

After sealing, each super panel 36 is again aligned using thecoordination holes. The overlapping portion of the panels 36, a lapjoint 48, is shown in FIGS. 2B and 2C. Each lap joint 48 has a pluralityof columns 50, where each of the columns 50 has 3 rows of rivets 52A-C.Two rivets of the rows 52A and 52C are for rivets that require acountersink as well as drilling.

The super panels 36 could be fastened to form a quarter panel by anassembly device, such as that described in U.S. Pat. No. 4,662,556 (the'556 patent). However, the device described in the '556 patent moves aworking unit along a guide beam that is supported by two huge arc-shapedgirders, and could not be used to form the lower or upper fuselage lobes38A and 38B, respectively, because of its size and design. Simply put,the unit described in the '556 patent or any variations thereof wouldnot fit within the fuselage lobes 35A and 38B, and certainly not thefuselage assembly 42. Attempts to redesign the assembly device discussedin the '556 patent to handle larger portions of the fuselage assembly 42have failed because of severe problems with vibration which interferedwith the proper seating of fasteners such as rivets. Further, theassembly device discussed in the '556 patent is not versatile andrequires an expensive and heavy support structure.

Presently, the fuselage quarter panels 36 and, lower and upper lobes 38Aand 38B, and the final fuselage assembly 42 are re-tacked into positionafter being filed, cleaned, and sealed. Then, the panels 36 are rivetedtogether by hand, where one person stands on a platform (not shown)outside the fuselage, inserting and then pneumatically driving a rivetfastener while another person stands inside the fuselage, bracing alarge bucking bar against a rivet shank and holding it in place byleaning against the bucking bar with his shoulder. Obviously, such aprocess presents a risk of injury. Further, the manual process resultsin rivets that were unevenly deformed, poorly seated, or riveted tooclose to an edge of the lap joint 48.

Unfortunately, the manual process is dangerous, time-consuming,expensive and often leads to extensive rework. Consequently, there is aneed in the art for a fastening system that speeds up production,ensures riveting and drilling accuracy, eliminates the required step ofdisassembling the entire fuselage to de-burr, clean and seal, and can beoperated within the final fuselage assembly 42.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a protrusion sensor determinesthe acceptability of a rivet within a component. The sensor includes abaseline detector which remains stationary, a movable detector whichmoves with a bucking bar module and produces a first signalproportionate to a distance between the baseline detector and themovable detector, and a CPU electronically connected to the movabledetector and receiving the first signal. The CPU determines whether therivet is acceptable by inputting a first distance when the bucking barmodule is clamping an inside surface of the component, inputting asecond distance when the bucking bar module is seated against a shank ofthe rivet, subtracting the second distance from the first distance todetermine a length of the shank protruding from the inside surface ofthe component, and comparing the length of the shank against an internaltable of rivet lengths to determine whether the proper rivet was loadedinto the component or whether the rivet is within an acceptabletolerance.

According to another aspect of the invention, a method is used to detectwhether a properly sized rivet was fed into a hole within an area of alap joint to be fastened. The method includes the steps of clamping thearea of the lap joint to be fastened with a bucking bar, measuring afirst distance from the end of the clamping bucking bar to a point fixedalong an axis normal to the lap joint, and inserting the rivet into thehole until a head of the rivet is flush with an outside surface of thelap joint and holding the rivet in this position. The method alsoincludes the steps of seating the end of the bucking bar against theshank of the rivet, measuring a second distance from the end of theseated bucking bar to the point fixed along the axis normal to the lapjoint, subtracting the second distance from the first distance to obtaina measured protruding shank length of the rivet, and comparing themeasured protruding shank length against a table of rivet lengths todetermine if the rivet placed in the hole in the inserting step was thecorrect size of rivet required.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the present invention willbecome better understood with regard to the following accompanyingdrawings where:

FIG. 1 is a perspective view of an assembled prior art super panel,showing skin, stringers, shear ties, stringer clips, and frame members;

FIG. 2A is a perspective view of a prior art fuselage lower lobe showinga floor grid;

FIG. 2B is a perspective view of a prior art completely assembledfuselage section;

FIG. 2C is a plan view of a prior art skin lap joint between two superpanels;

FIG. 3 is an end view of a mini-riveter system of the present invention;

FIG. 4A is a side view of an index pin of the mini-riveter system;

FIG. 4B is a front view of the index pin;

FIG. 4C is a front view of a reflective head of the index pin;

FIG. 5 is a perspective view of external guide rails and an outsideend-effector subsystem of the mini-riveter system;

FIG. 6 is a schematic diagram of a plurality of vacuum generators of theexternal guide rails;

FIG. 7 is a plan view of a contact portion, including vacuum seals ofthe primary guide rails of the external guide rails;

FIG. 8A is a perspective view from the upper left of the outsideend-effector;

FIG. 8B is a perspective view from the lower left of the outsideend-effector;

FIG. 8C is a perspective view from the upper right of the outsideend-effector;

FIG. 8D is a perspective view from the lower right of the outsideend-effector;

FIG. 8E is a perspective view of the bottom of the outside end-effector;

FIG. 9A is a perspective view of a pressure foot subassembly of theoutside end-effector;

FIG. 9B is a side view of a frame and a mid-linkage of the pressure footsubassembly;

FIG. 10A is a bottom view of a fastener feed fingers of the outsideend-effector;

FIG. 10B is a side view of the fastener feed fingers of the outsideend-effector;

FIG. 11 is a perspective view of the inside end-effector and internalguide rails of the mini-riveter system;

FIG. 12A is a perspective view of the inside end-effector;

FIG. 12B is a perspective view of the bottom of the inside end-effector;

FIG. 13A-13C are side views of a rivet protrusion sensor of the insideend-effector, where:

FIG. 13A shows a bucking bar at initial clamp-up;

FIG. 13B shows a bucking bar just prior to deformation;

FIG. 13C shows a bucking bar seated against a button upon completion ofa fastening cycle;

FIG. 14A is a perspective view of a straight bucking bar;

FIG. 14B is a perspective view of a left-handed bucking bar;

FIG. 14C is a perspective view of a right-hand bucking bar;

FIG. 14D is a side view of a left-hand bucking bar inserted between alap joint and a stringer;

FIG. 15 is a perspective view of a system cart including a controlsystem of the mini-riveter system;

FIG. 16 is a flow chart showing a main operational routine implementedby a control processing unit (CPU) of the control system;

FIG. 17 is a flow chart showing a clamping and drilling subroutineinvoked by the operational routine; and

FIG. 18 is a flowchart showing a fastening subroutine invoked by theoperational routine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions:

Airframe: the structural assembly that comprises the body of an airplanewithout wings or horizontal and vertical stabilizers;

Boelube: Cetyl alcohol, a nontoxic lubricant used for metal cutting;

Bucking Bar: A metal tool used to flatten the rivet's shank into adriven button during the riveting process. The bucking bar is used as ananvil to react the forces being driven into the rivet with a rivet gun,thus deforming the rivet;

Clamp-Up: Hold two or more pieces of the airframe together so that thereare no gaps between the principal surfaces; the ability to hold the workpieces together;

Countersink Depth: Depth of countersink in a fastener hole;

Countersinking: Machining of a conical hole coaxial with a through-holefor purposes of accepting a fastener head that will be flush (i.e.; thesame height as) with the material surrounding the hole;

Dwell Time: A period of time that is permitted to elapse as part ofnormal fastening operations: e.g.; for sealant squeeze out, formaintaining power to the rivet gun during rivet driving, etc;

End-Effector: A tool positioner with modules installed;

E-Stop (Emergency Stop): A software-independent stop signal that causesthe system to stop immediately upon activation;

Fail-Safe: Incorporating some feature for automatically counteractingthe effect of an anticipated possible source of failure; having nochance of failure; infallible, problem-free;

Fasteners: The generic term used to describe rivets and bolts;

Feed-hold: A software-controlled stop of the system at any point in theprocess; (Power to motors and drives should not need to be removed.)

Lap Joint: An area of overlap between two panels to be fastened, wherecolumns of rivets are installed along a length of the lap joint and rowsof rivets are installed along the width of the lap joint.

Machine Control Data (MCD): The program that is loaded into thecontroller that directs the operation of the MRS in performing the lapfastening process;

Modal: Numerical Control (N/C) operating modes that are maintained(latched) in an acting state for all subsequent operations untilmodified by another N/C command;

Module: An independently operable unit that is part of the total system.Examples are the drill/countersink module, the rivet drive and feedmodule;

Rc (Rockwell "C"): A standard method of measuring and designating thehardness of metals;

Rivet: A metal bolt or pin used to join two or more objects by insertingit through a hole in each object and then hammering the narrow end toform another head (or button);

Sealant: A durable, waterproof material applied to selected assembliesto prevent water from infiltrating and aiding in the corrosion of thoseassemblies;

Software Source Code: The editable software scripts that a softwaredeveloper writes for a computer application;

Stay-Within Envelope: An imaginary envelope that the system, whenmounted on guide rails installed on an airframe, must not extend beyond.

Swirl Marks: Marks into the surface of a material that is being drilledthat are concentric with the hole. The cutaway material that is beingexpelled from the hole causes swirl marks; and

Workpiece, Component, Panel: Airframe or any structure or item that thesystem will perform elements of the fastening process on.

Mini-Riveter System

The present invention relates to a mini-riveter system capable ofquickly and accurately fastening two panels at a lap joint without theuse of large cumbersome machinery.

As shown in FIG. 3, the mini-riveter system 100 includes external guiderails 102, supported by and positioned on an outside surface of theoverlapped panels 110, and an outside end-effector subsystem 104 movablealong the external guide rails 102, for clamping the panels 110,drilling/countersinking the panels 110, fastener feeding/insertion intothe panels 110, and driving a rivet to fasten the panels 110. Themini-riveter system 100 also includes internal guide rails 106,supported by and positioned on an inside surface of the panels 110, andan inside end-effector subsystem 108, movable along the internal guiderails 106, for clamping the panels 110 and bucking a rivet to fasten thepanels 110, even when the fastener is obstructed by a feature attachedto one of the panels 110.

The mini-riveter system 100 is easily transportable on a control systemcart 112, as shown in FIG. 15, which supports a control system 114. Thesystem 100 is capable of being quickly installed onto the two panels 110without special tooling support requirements. Further, the system 100 iscompact enough that it can be easily installed and moved around theinside and outside of an airframe fuselage section. Finally, the system100 is flexible enough to fasten individual panels, combinations ofpanels, subsets of an airframe fuselage, or an entire airframe fuselage.

The outside end-effector 104 and the inside end-effector 108, as shownin FIG. 3, clamp down a portion of a lap joint 116 formed by the twopanels 110 in a localized manner without interfering with other nearbyoperations. Further, the localized pressure extended during the clampdown prevents burring and keeps chips from falling between the lap joint116. Thus, the localized pressure allows the steps of sealing anddrilling the lap joint 116 to be immediately followed by the step offastening the lap joint 116. This quick process replaces the formerprocess of untacking drill components, filing them, cleaning them,sealing them and re-tacking and aligning them and then fastening thepanels 110 together at the lap joint 116.

The system 100 also offers a high degree of modularity, allowing quickand easy replacement of drills, countersinks, rivet guns, and buckingbars. This arrangement provides a high degree of flexibility and enablesthe system 100 to accommodate a large percentage of fastening tasksrequired on an air frame.

The small size and light weight of the mini-riveter system 100 makes itideal for gang fastening, where multiple versions of the system 100 areinstalled at various positions along a larger mechanical structure, suchas an airframe to conduct simultaneous operations on the same lap joint,or to conduct simultaneous operations on different lap joints of thestructure/airframe fuselage. This capability of the system 100significantly improves the production flow rate of an aircraft fuselage.

Unlike prior art fastening devices which home or zero their coordinatesystems on a fixture, the mini-riveter system 100 is able to home on thecoordination holes being used to align the two panels 110. The use ofthe coordination holes to home the inside end-effector 104 and theoutside end-effector 108 increases both the end-effectors' accuracy, andby re-homing the inside and outside end-effectors 104 and 108,respectively, at each of the coordination holes along a lap joint 116,drift due to thermal change or fastener-induced growth is minimized.

Direct Index Pins:

The mini-riveter system 100 homes or zeros in on the same coordinationholes used to align the overlapping panels 110 at the lap joint 116. Toaccomplish this, direct index pins 120, as shown in FIGS. 4A-4C, areinstalled in the coordination holes at the lap joint 116. The directindex pins 120 include a protruding key 122, having a threaded shankthat snugly fits within the coordination holes, as well as a portionthat extends from the outside surface of the lap joint 116, having anouter lip 124 used to align the external guide rails, and recess 125used to home the outside end-effector 104. The direct index pins 120also include a reflective head 126 that threadingly engages the shank ofthe protruding key 122. The reflective head 126, which extends out fromthe inside surface of the lap joint 116, includes a reflecting square128, used to home the inside end-effector 108. The reflecting square hasa width w in parallel with the length of the lap joint 116.

The mini-riveter system 100 establishes a positioning referencecoordinate system relative to the index pins 120 installed in the lapjoint 116. The use of the index pins 120 allows the establishment oflocal coordinate points to re-zero both the outside end-effector 104 andthe inside end-effector 108. By periodically re-zeroing theend-effectors, the likelihood of improper positioning of holes andfasteners due to growth or distortion along the lap joint 116 isdramatically reduced. Also, by homing on the coordination holes, thereis no need for a fixture to home the end-effectors. The use of a fixturewhich would reduce the overall advantages gained by aligning componentswith coordination holes.

External Guide Rails:

The external guide rails 102, as shown in FIG. 5, include a primary rail130, a secondary rail 132, and a plurality of rail ties 134A-134C. Therail ties 134A-134C are each aligned to the key 122 of one of the indexpins 120. Then, the rail ties 134 are coupled to the primary andsecondary rails 130 and 132, and are used to align the primary andsecondary rails 130 and 132 to the lap joint 116.

The primary rail 130 and the secondary rail 132 each have a tube portion135A and 135B, respectively, for slideable engagement with the outsideend-effector 104, as well as respective primary and secondary contactplatforms 136A and 136B, for contact with the lap joint 116. The tubeportions 135A and 135B are mechanically coupled to their respectivecontact platforms 136A and 136B.

The contact platforms 136A and 136B each have a plurality of lips138A-138F, respectively, each extending toward the lap joint 116. Eachof the lips 138A-F have a threaded hole 140, used to align the rail withits respective one of the rail ties 134A-C

Vacuum System:

The contact platforms 136A and 136B, as shown in FIG. 5, include avacuum system having a plurality of vacuum generators 144A-F. FIG. 6 isa schematic diagram of the vacuum generators 144A-144C for the primarycontact platform 136A, where each of the generators 144A-144C,respectively, has a vacuum pump 146A-146C, a vacuum gauge 148A-148C, anda vacuum switch 150A-150C. The vacuum generators 144A-144C arepreferably PIAB™ generators (Part No. X 10). Each of the vacuumgenerators 144A-144C is in pneumatic communication with correspondingrubber gasketed vacuum pads 152A-152C, shown in FIG. 6, which arelocated on a side of the contact platform 136A contiguous with thepanels 110 forming the lap joint 116. The secondary contact platform136B has identical vacuum pumps 146D-146F, vacuum gauges 148D-148F andvacuum switches 150D-150F, as well as vacuum pads 152D-152F.

The tube portions 135A and 135B are hollow and carry an air flowpressurized to approximately 90-100 psi. The air is supplied off thetube portions 135A and 135B via air taps (not shown) to the vacuumgenerators 144A-144C, and 144D-144F, respectively, of the primary andsecondary platforms 136A and 136B. The positive air pressure supplied bythe tube portions 135A and 1355B expands in one or more orifice ejectornozzles (not shown) of the vacuum generators 14A-144F, convertingpressure and heat energy into motion energy. The compressed air jetincreases speed rapidly, while the pressurized temperature of the airdecreases, inducing a high vacuum flow, thereby creating a vacuum on asuction side of the vacuum pumps 146A-146F. Both the primary rail 130and the secondary rail 132 connect and operate in the same manner, wherethe vacuum generators 144A-144F produce a vacuum in corresponding vacuumpads 152A-152F. The vacuum pads are isolated from one another so if oneof the pads 152A-152F is lost, it will not affect the vacuum in theremaining pads.

As shown in FIG. 6, each of the vacuum generators 144A-144F has apneumatic logic circuit including three AND gates 154A-154C, and threevacuum switches 150A-150C. The logic circuit verifies that a vacuum hasbeen produced by a particular vacuum generator. When the vacuum pads152A-152F have reached an acceptable level of vacuum, the pneumaticlogic circuit creates and sends a vacuum present signal to the nextvacuum generator 144. Each logic circuit "AND's" the previous vacuumsignal with the current vacuum signal and sends it on to the next vacuumgenerator 144. The process repeats until the entire rail has beenchecked and the resulting signal is sent to the CPU 398 for processing,leading to a warning display or an E-stop system shutdown.

The vacuum applied by the vacuum generators 144A-144F must be sufficientto couple the external guide rails 102 to the lap joint 116 while it issupporting the outside end-effector 104, as shown in FIG. 5. Thecoupling force to the panels 110 forming the lap joint 116 must besufficient for the external rails 102 to transfer up to 700 lbs. offorce generated by the outside end-effector 104 to the panels 110 duringfastener operations.

The vacuum system allows the external guide rails 102 to be completelysupported by the panels 110 forming the lap joint 116 without the needof a support fixture. This allows the system 100 to be brought to anypart being worked on, even when a joint is located in an inconvenientarea that would not admit fixturing or large automated machinery. Also,because the external rails 102 are vacuum coupled to the lap joint 116,the external rails 102 follow the contour of the panels making up thejoint, keeping the outside end-effector relatively normal to it.Further, since the vacuum pads 152A-152F are made of neoprene or rubber,the panels are not damaged during fastener operations.

The removable rail ties 134A-134C each include receptacles 156A-156C forengaging a key 122 of a respective one of the index pins 120. Once oneof the receptacles 156A-156C has been engaged with the key 122, itpositions the rail tie 134 in appropriate x,y coordinates relative tothe lap joint 116. As shown in FIG. 5, the rail tie 134B, like each ofthe rail ties 134A-134C has two hand-tightened bolts 158A and 158B, thatthreadingly engage the threaded holes 140 in the lips 138B and 138E ofthe primary rail 130 and secondary rail 132, respectively. The bolts158A and 158B properly locate the primary rail 130 and secondary rail132 along the x-axis. Once corresponding bolts of another rail areengaged to their respective lips, the primary rail 130 and secondaryrail 132 are also aligned along the y-axis.

The arrangement of the external guide rails 102 allows it to be entirelysupported by the panels 110 forming the lap joint 116 using coordinationholes 142 as reference points. The rail ties 134A-134C are aligned withtheir respective coordination holes using the key 122 of the index pins120. The rail ties 134A-134C are then fastened to the primary rail 130and the secondary rail 132, using features, i.e. the coordination holes,of the panels 110 as the only means of aligning the external rails 102to the lap joint 116. Thereafter, the vacuum is applied, causing theexternal rails 102 and the outside end-effector 104 to be entirelysupported by the panels 110 forming the lap joint 116.

Outside End-Effector Subsystem

The outside end-effector subsystem 104, as shown in FIGS. 8A-8E,includes an outside end-effector engagement assembly for lifting theoutside end-effector 104 and slidingly engaging the outside end-effector104 onto the external rails 102. The outside end-effector 104 alsoincludes an outside tool positioning assembly for positioning modularcomponent, such as drills and fasteners, relative to the indexing pins120. The outside tool positioning assembly includes an external positiondetection subassembly, for detecting the indexing pins 120 and formeasuring the distance traveled by the outside end-effector 104 from thelast homed position. The outside tool positioning assembly also includesan outside end-effector drive subassembly for moving the outsideend-effector 104 along the x-axis on the external guide rails 102, and apressure foot subassembly 236 for clamping the lap joint at the areawhere a fastening operation is to occur. The outside end-effector 104further includes a module movement subassembly 250 for positioning adrill/countersink module and a rivet drive/fastener feed module.

Outside End-Effector Engagement Assembly:

The outside end-effector engagement assembly, as shown in FIGS. 8A and8D, includes a primary handle 200, and a secondary handle 202, which areused by an operator to lift the outside end-effector 104 onto theprimary rail 130 and the secondary rail 132.

The outside engagement assembly also includes a primary clamshellbearing system 204, and a secondary clamshell bearing system 206, asshown in FIG. 8D, for allowing the outside end-effector 104 to beinstalled or removed anywhere along the length, i.e. x-axis, of theexternal guide rails 102. A primary pivot arm 208 of the primary bearingsystem 204 is opened or closed on the primary rail 130 by a primary aircylinder 212, as shown in FIG. 8D. In the same manner, a secondary pivotarm 210, of the secondary bearing system 206 is opened or closed on thesecondary rail 132 by a secondary air cylinder 214, as shown in FIG. 8C.

In a preferred embodiment, the primary and secondary pivot arms 208 and210 can be locked closed to prevent the outside end-effector 104 fromfalling off the external guide rails 102 if the unit were to experiencean air pressure loss condition. This is accomplished by using a lockingair cylinder (not shown) to move a tool pin (not shown) through theprimary and secondary arms 208 and 210, respectively, and the main body216 of the outside end-effector 104. The tool pin keeps the pivot armsfrom opening when pressure is lost. An optional push button (not shown)located on the main body 216 allows the operator to operate the lockingair cylinder at will.

Outside End-Effector Tool Positioning Assembly:

External Position Detection Subassembly:

The external position detection subassembly, as shown in FIG. 8A,includes a homing sensor 218, and a final external position encoder 220.

The homing sensor 218, shown in FIG. 8A, is preferably a proximitysensor. When requested by the CPU 398, the homing sensor 218 detects thegap 125 within the key 122 of the selected one of the index pins 120being homed to and re-establishes, i.e. re-zeros, its x,y coordinatesystem based on the nearby detected index pin 120. Preferably, whenoperating on an aircraft fuselage, the control system 114 will requestthe homing sensor 218 to locate an index pin 120 along the fuselage,i.e. re-zero, at every bay of the fuselage, where a bay is defined bytwo frames of the aircraft fuselage. By re-zeroing at every bay,inaccuracies from either fastener-induced growth of material ortemperature variation can be significantly reduced. Thus, the outsideend-effector 104 can maintain a high degree of positional accuracy byperiodically re-calibrating its alignment based on the same structure ofpanels 110 forming the lap joint 116 which supports the outsideend-effector 104.

The final external position encoder 220, as shown in FIGS. 8A and 8B,comprises a plurality of first wheels 222A-222C which engage above andbeneath the primary rail 130. The first wheels 222A-222C move when theoutside end-effector 104 moves relative to the primary rail 130. Theexternal encoder 220 operates in a closed loop system reporting theposition of the outside end-effector 104 to the control system 114relative to the last homed position.

Outside End-Effector Drive Subassembly:

The outside end-effector drive subassembly for moving the outsideend-effector 104 along the x-axis on the external guide rails 102, asshown in FIGS. 8C and 8D, includes a first friction drive wheel 224, afirst friction air cylinder 226 for engaging the first friction drivewheel 224 to the primary rail 130. The first friction drive wheel 224 isrotated by an x-axis servo-motor 228 which drives the outsideend-effector 104 along the x-axis. Since the first friction drive wheel224 has no gears or teeth, no damage will occur to the lap joint 116 orthe mini-riveter system 100 if the outside end-effector 104 encountersan obstacle while traveling along the x-axis. Instead of burning out amotor or "chewing up" components, the first friction drive wheel 122simply spins in place without causing any damage. The external encoder220 reports the location of the outside end-effector 104 to the controlsystem 114 which, in turn, deactivates the x-axis servo-motor 228 when adesignated position is reached.

Pressure Foot Subassembly:

The pressure foot subassembly 230, shown in FIGS. 8C-8E, 9A and 9B,applies a clamping pressure to a relatively small area of the lap joint116 in support of fastening and drilling operations.

The pressure foot subassembly 230 includes a porthole clamp 232, shownin FIG. 9A having an orifice 234 sized to allow passage of a drill,countersink, or fastening device. The porthole clamp 232 is pressedagainst a relatively small area of the lap joint 116 to apply pressurearound an area to be drilled and fastened. Preferably, the portholeclamp 232 is steel hardened to at least Rc 65, and is polished to 16 Rhror smoother to prevent scratches to the panels 110 during clamp-up.

The pressure foot 230 also includes a U-shaped frame 235, shown in FIGS.8E and 9B. A lower arm 238 of the frame 236 is coupled to the portholeclamp 232. A mid-linkage 242 flexibly couples an end of an upper arm 240and an end of the lower arm 238. The mid-linkage 242 includes a joint244, which is in physical contact with a clamping air cylinder 246. Whenthe clamping air cylinder 246 is extended, the mid-linkage 242 and theU-shaped frame 236 are expanded, causing pressure to be applied betweenthe outside end-effector 104 and the lap joint 116.

A sensor 248, as shown in FIG. 9B, is capable of detecting clamp-upforces applied to the lap joint 116 of up to 700 lbs. Preferably, thepressure foot 230 via the porthole clamp 232 is capable of providing amanually adjustable clamp-up pressure ranging from 100-500 lbs. Foroptimal results a pressure of 300 lbs. is applied. Further, in apreferred embodiment, the dwell time of the clamp 232 prior to drillingis between 1 and 20 seconds.

By applying clamp-up pressure to a localized region during drilling,there is no burring occurring between the panels 110 of the lap joint116. If an inner burr were produced and allowed to remain, it wouldgreatly reduce the fatigue life of the panels 110. Further, no chips orshavings are falling between the panels 110 of the lap joint 116. Thus,the panels 110 need not be disassembled, filed/de-burred, cleaned,sealed, and then reassembled as previously required. The elimination ofthese steps affords a significant savings in time and cost. Further, theuse of a clamp-up system that mounts on the parts/panels 110 beingassembled is unique and allows a much more flexible clamp-up system.

The pressure foot subassembly 230, as shown in FIG. 8E, is moved alongthe y-axis from row to row of rivets along the width of the lap joint116 by a clamp air motor 248 and a clamp ball screw 250. The position ofthe subassembly 230 is determined by a LVDT position measuring device251 connected to the pressure foot 230, as shown in FIG. 9A. The controlsystem 114 reads a signal produced by the LVDT device 251 to verify theposition of the porthole clamp 232. If the porthole clamp 232 is out ofposition, then an air valve (not shown) is actuated to drive the clampair motor 248 which then moves the porthole clamp 232 into the correctposition.

Module Movement Subassembly:

The outside end-effector 104 uses the module movement assembly 250,shown in FIGS. 8C-8E to align a machine axis of a drill/countersinkmodule 252 or a rivet drive/fastener feed module 254 with the orifice234 of the porthole clamp 232 and the section or area of the lap joint116 to be fastened.

The module movement assembly 250 includes an external module carriage256 slidingly engaged with the main body 216 of the outside end-effector104 along a linear bearing 258. A module servo-motor 260 moves thedrill/countersink module 252 and the rivet drive/fastener feed module254 from a position where the drill/countersink module 252 was alignedto operate to a position where the rivet drive/fastener feed module 260is aligned to operate, from row to row along a selected column ofrivets.

Drill/Countersink Module:

The drill/countersink module 252, as shown in FIGS. 8A-8E, prepares aposition or area of the lap joint 116 for receiving a fastener bydrilling and countersinking a hole at the position. The drill module 252includes drill unit 262 which is pneumatically driven, andinterchangeable. The drill unit 262 maybe interchanged with a differentsized unit by removing it from a drill holder 264 which is horizontallyfixed and vertically slidable relative to the external carriage 256 ofthe module movement assembly 250. The drill unit 262 is removed from thedrill holder 264 by unscrewing a quick release drill knob 266, as shownin FIG. 8A.

The drill unit 262 rotates an integral drill bit and countersink 268, asshown in FIGS. 8C and 8E. The integral drill bit and countersink 268allows the position of the lap joint 116 to be both drilled andcountersunk with one plunge of the drill unit 262.

The drill/countersink module 252 further includes first and secondpneumatically powered drill plunging air cylinders 270 and 272,respectively, coupled to the external carriage 256 of the modulemovement assembly 250 and the drill holder 264 for moving the drill unit262 along the z-axis normal to the lap joint 116. The drill module 252includes a stop 274 to limit the motion of the integral drill bit andcountersink 268 into the lap joint 116 to provide the desirablecountersink depth. The stop 274 also acts as a fail safe, preventingoverdriving of the drill bit and countersink 268 into the lap joint 116.A Boelube reservoir 275, shown in FIGS. 8A and 8C, provides lubricantduring the drilling process to enhance hole quality and extend the lifeof the drill bit and countersink 268.

Rivet Drive/Fastener Feed Module:

The rivet drive/fastener feed module 254, as shown in FIGS. 8A-8E, loadsa rivet/fastener into a hole drilled by the drill module 252 and thenupsets the rivet in the hole in a manner that assures a high degree ofaccuracy, preventing rework.

The rivet module 284 includes a rivet drive unit 276, which ispneumatically driven and interchangeable. The rivet drive unit 276 maybe interchanged with a different drive unit, allowing the rivet module254 to accommodate various fastener requirements. The interchange of thedrive units is accomplished by removing the rivet drive unit 276 from arivet drive holder 278, which is horizontally fixed and verticallyslideable relative to the external carriage 256 of the module movementassembly 250, and replacing it with a new rivet unit. The rivet driveunit 276 is removed from the rivet drive holder 278 by unscrewing firstand second quick release rivet knobs 280A and 280B, respectively, asshown in FIG. 8A.

The rivet module 254 further includes a first and second pneumaticallypowered rivet seating plunger 282 and 284, respectively, as shown inFIG. 8D, coupled to both the rivet drive holder 278 and a cylindricalportion 279 of the external carriage 252 for moving the rivet unit 276along the z-axis. The rivet drive unit 276 drives a rivet driver head(not shown) used to impact a head of the rivet, resulting in thedeformation/upsetting of the rivet. The first and second rivet seatingplunger 282 and 284 seat the rivet driver head against the head of therivet to be upset.

The rivet module 254 also includes a fastener supply system. A pluralityof rivets are sorted and queued by a vibratory bowl 286, shown in FIG.14, and pneumatically (using air pressure) fed to the rivet module 254via feed tubes 288A and 288B.

The rivets delivered by the rivet feed tubes 288A and 288B are fed to aset of fastener feed fingers 290, as shown in FIGS. 8E, 10A and 10B. Therivet fingers 290 are pneumatically powered to hold the rivet while itis inserted into the hole to be fastened.

As shown in FIGS. 10A and 10B, the feed fingers 290 include a circularstructure 291, having an inner orifice, where four fingers 292A-292D areattached to a respective side of the inner orifice of the circularstructure 291. The feed fingers 290 lower the rivet into the hole to befastened using the first and second pneumatic seating plungers 282 and284, respectively.

Interfaces:

The outside end-effector 104 also includes a plurality of electrical andpneumatic interfaces. For example, a plurality of pneumatic andelectrical connections are located at bottom connectors 294, shown inFIG. 8D and 8E. The pneumatic bottom connectors 294 supply air to theair cylinders, pneumatic riveter and drill units discussed above. Theelectrical group of the bottom connectors 294 supply power to theabove-discussed servo motors, and the power is distributed via anelectrical service box 296, shown in FIG. 8A. Preferably, the bottomconnectors are quick disconnects allowing the outside end-effector 104to be easily moved, serviced, and installed.

Internal Guide Rails:

The internal guide rails 106, as shown in FIG. 11, are positioned on theinside surface of the lap joint 116. The internal guide rails 106support the inside end-effector 108 and transfer forces generated by theinside end-effector 108 during fastening operations to the panels 110forming the lap joint 116.

The internal guide rails 106 include an upper rail 300 and a lower rail302. Each of the upper and lower rail 300 and 302, respectively,includes an upper and lower tube portion 304A and 304B, for slideableengagement with the inside end-effector 108. The upper and lower-rail300 and 302 also have an upper and lower bar portion 306A and 306B,which are mechanically coupled to the respective tube portion 304A and304B. The upper and lower bar portions 306A and 306B are coupled to aplurality of upper and lower attachment brackets 308A-308C, and310A-310C, respectively, as shown in FIG. 11.

Attachment Brackets:

As shown in FIG. 11, the upper guide rail 300 is hung by the upperattachment brackets 308A-308C by hooking the brackets 308A-308C to afeature previously coupled to the inside surface of the panels 110forming the lap joint 116. In a similar manner, the lower guide rail 302is stood upon the attachment brackets 310A-310C. In one embodiment, asshown in FIG. 11, the present system is used within an aircraft fuselagesection where the features include a plurality of stringers 311positioned horizontally at intervals along the inside surface of thepanels 110 and intersected by a plurality of frames 312 defining thebays within the fuselage section.

The attachment brackets 308A-308C and 310A-310C are hooked behind aT-shaped portion of the stringers 311 and adjacent to one of the framemembers 312. As shown in FIG. 11, the attachment brackets 308A-308C and310A-310C are each clamped to the stringers 311 with respective circularplates 314A-314F, and 315A-315F, which contact a face of the stringers311 and respective hooks 316A-316F and 317A-F, which reach behind theT-portion of the stringer 311. Respective levers 318A-318F and 319A-319Fdraw the circular plates 314A-314F, 315A-315F and the hooks 316A-316F,317A-317F together to lock both the upper and lower guide rails 300 and302 onto their respective stringers 311.

The attachment brackets 308A-308C and 310A-310C, as shown in FIG. 11,attach the internal guide rails 106 to the inside surface of the panels110, or airframe, forming the lap joint 116. In the present embodiment,the stringers 311 and frame members 312 are aligned by coordinationholes. Therefore, the internal guide rails 106 will benefit from theself aligned features coupled to the panel skins 110 and will, in turn,be aligned with the lap joint 116 without the need for externallysupported fixturing.

In an alternative embodiment, the attachment brackets 308A-308C and310A-310C may be varied in length or be adjustable in length of allowattachment to irregular features coupled on the inside surface of thepanels 110. If the inside surface has no features, then theabove-described vacuum generators and pads could be used to replace theattachment brackets 308A-308C and 310A-310C.

The arrangement of the internal guide rails 106 allows an end-effectorto be installed inside a fuselage or other restricted area which wouldnot normally support a fixture or large mechanism required to accomplishthe same task.

Inside End-Effector

The inside end-effector 108, as shown in FIGS. 12A and 12B, includes aninside end-effector engagement assembly for allowing the insideend-effector 108 to slide along the internal guide rails 106, an insidetool positioning assembly for accurately positioning bucking bar modulesalong an x'-axis (parallel to the inside guide rails 106) relative tothe index pins 120 inserted in the lap joint 116, and a rotationalcarriage assembly for moving the bucking bar modules along a y'-axis(perpendicular to the inside guide rails 106) relative to the index pins120.

Engagement Assembly:

The inside end-effector engagement assembly includes four insidestandard bearings 320A-320D, as shown in FIGS. 12A and 12B. The insideend-effector 108 is loaded at the outside end of the internal guiderails 106 by threading the internal guide rails 106 into the areadefined by the standard bearings 320A-320D. By locking the insideend-effector 108 to the internal guide rails 106 in this manner, theinside end-effector 108 is fail safe, and much lighter in weight than aunit locked in place with air cylinders.

Tool Positioning Assembly:

The tool positioning assembly includes an internal position detectionsubassembly, and an inside end-effector drive subassembly 336.

Internal Position Detection Subassembly:

The internal position detection subassembly, as shown in FIG. 12B,includes an internal homing sensor 322 having first and secondhelium-neon lasers 324A and 324B, and respective first and second ChargeCoupled Devices (CCD's) 326A and 326B. The first and second lasers 324Aand 324B are directed toward the reflecting square 128 of the index pins120 and their beams are parallel and spaced a distance just short of thewidth of the reflecting square 128, between 1 and 5 mm, preferably 3 mm.Accordingly, as the inside end-effector is moved along the length of thelap joint 116 when both the first and second CCD's 326A and 326Bsimultaneously read their respective laser beams as being reflected bythe reflecting square 128, the inside end-effector 108 has been homed toa zero position on the x', y' coordinate system defining the insidesurface of the lap joint 116. Preferably, the determination that theinside end-effector 108 has been homed is made by the control system114.

The internal position detection subassembly also includes an internalfinal position encoder 328, shown in FIG. 12B, which determines thedistance A x' that the inside end-effector 108 has traveled along theinternal guide rails 106 from the last measured home position, asdefined by the index pins 120.

The internal encoder 328, as shown in FIGS. 12A and 12B, includes atwo-wheel detector 330 that moves relative to the upper guide rail 130,where the number of rotations and hence the distance traveled by thedetector 330 is indicated by a signal to the control system 114 and isused to determine the position of the inside end-effector 108. As shownin FIGS. 12A and 12B, the two-wheel detector 330 is engaged with theupper rail 300 using a detector air cylinder 332 which, when activated,pivots an arm 334 causing the two-wheel detector 330 to move against theupper rail 300.

Inside End-Effector Drive Subassembly:

The inside end-effector drive subassembly 336, as shown in FIG. 12A,moves the inside end-effector 108 along the internal guide rails 106.The inside drive subassembly 336 includes an internal friction drivewheel 338 which is driven by an x' axis servomotor 340. The use of theinternal friction drive wheel 338 eliminates problems encountered whenusing gears or teeth. If the inside end-effector 108 were to encounteran obstacle, the internal friction drive wheel 338 would simply spin inplace without causing any damage to either the inside end-effector 108or the internal guide rail 106.

The internal friction drive wheel 338 is engaged with the upper rail 300by a second drive air cylinder 342 which, when activated, pivots a drivearm 344, causing the internal friction wheel 338 to move up against theupper rail 300.

Rotational Carriage Assembly:

The rotational carriage assembly of the outside end-effector 108 rotatesa left-hand (LH) bucking bar 350 and a right-hand (RH) bucking bar 352,as shown in FIG. 12B, relative to an inside frame 354 and the upper andlower guide rails 300 and 302, respectively.

Bucking Bar Modules:

The rotational carriage assembly includes a LH bucking bar module 356and a RH bucking bar module 358, as shown in FIGS. 12A and 12B.

Both the LH bucking bar module 356 and the RH bucking bar module 358include LH and RH quick release knobs 360A and 360B, respectively, asshown in FIG. 12A, allowing the two bucking bars to be easilyinterchanged with bucking bars having bucking dies of different shapes,sizes, and materials suited to a particular task. With this arrangement,the bucking bars can be easily swapped on the fly.

Further, the LH bucking bar module 356 and the RH bucking bar module 358include a LH retract/extend cylinder 362A, and a RH retract/extendcylinder 362B, respectively. The LH and RH retract/extend cylinders 362Aand 362B are pneumatically driven, and respectively cause the LH buckingbar 350 and the RH bucking bar 352 to move along the Z' axis normal tothe lap joint 116 on the inside surface of the panels 110.

Protrusion Sensor:

The LH and RH bucking bar modules 356 and 358, respectively, alsoinclude a LH protrusion sensor 364A and RH protrusion sensor 364B, asshown in FIGS. 12A, 12B and 13A-C, which are used to measure the lengthof the shank of a rivet 372 protruding from the inside surface of thelap joint 116.

The LH and RH bucking bar modules 356 and 358 move the respective LH andRH bucking bars 350 and 352 along the z' axis to three basic positions.In a first position, the LH and RH bucking bars 350 and 352,respectively, are fully retracted to clear away from obstructivefeatures attached to the inside surface of the panels 110, allowing theinside end-effector 108 freedom of movement. In the second position, asshown in FIG. 13A, one of the bucking bars 350 and 352 is clampedagainst the inside surface of the panels 110 against an area to befastened prior to and during a drilling operation. During thisoperation, the protrusion sensors 364A and 364B measure a distance (d1)from a fixed sensor component 368A and 368B. In the third position, oneof the bucking bars 350 and 352 is driven against a shank 366 of a rivet372 inserted into the newly drilled hole used to fasten the position ofthe lap joint 116. Here, the protrusion sensor 364A measures a distance(d2) from the fixed sensor component 368A. The two values (d1) and (d2)are sent to the control system 114, which processes this information todetermine the length of the shank 366 protruding from the insidesurface. The length of the shank 366 is compared against a table valueof rivet lengths to determine whether the proper rivet has beeninstalled in the hole and, if so, whether it is in tolerance.

As shown in FIG. 13C, the LH protrusion sensor 364A continues to monitorthe length (d3) of the shank, as it is deformed into a button 370. In apreferred embodiment, the signal from the LH protrusion sensor 364A isprocessed by the control system 114 to determine when a proper sizedbutton has been formed (i.e., d3=proper button size indicated by table)and to immediately stop the rivet driver unit 276 from upsetting therivet. This feedback system ensures a properly sized and seated rivetfor each fastening operation.

The operation of the RH bucking bar module 358 and the RH protrusionsensor 364B operate in an identical manner to the LH bucking bar module356 and the LH protrusion sensor 364A, as described above and shown inFIGS. 13A-13C.

Bucking Bar Dies:

The LH and RH bucking modules 356 and 358, respectively, hold andposition the LH and RH bucking bars 350 and 352. Either of the LH or RHbucking modules 356 and 358, respectively, can hold and position astraight bucking bar 371, as shown in FIGS. 13A-13C, and 14A. Thestraight bucking bar 371 can be swapped with either the LH or RH buckingbars 350 and 352, when the inside end-effector 108 is upsetting a rivet,such as the rivet 372 shown in FIG. 13B, that is not obstructed by aT-shaped portion 374 of the stringer 311. The straight bucking bar 371has a die with a first gap 376 for receiving a drill bit during thedrilling operation. The alignment of the first gap 376 and the drill bitextends the life of the drill bit and countersink 268 as well as thestraight bucking bar 371.

To solve the problem of fastening obstructed rivets, such as a top rivet378 shown in FIG. 13A, the LH and RH bucking modules 356 and 358,respectively, cause the LH and RH bucking bars 350 and 352,respectively, to rotate behind the T-shaped portion 374 of the stringer311, as shown in FIG. 14D. The LH and RH bucking bars 350 and 352 eachinclude a LH and RH aluminum arms 380A and 380B, and LH and RH"L-shaped" bucking dies 382A and 382B, as shown in FIG. 12B, 14B, and14C. The LH and RH "L-shape" of the bucking dies 382A and 382B allow thedies to slide behind an obstruction, such as the T-portion 374 of thestringer 311. The bucking dies 382A and 382B may have double offsetsbuilt therein, where one offset is for getting behind frames and theother offset is forgetting behind the stringers 311.

Conventional bucking dies are formed from steel. Unfortunately, when theL-shaped dies are formed from steel, the rivets formed using these diesare severely clinched (i.e. clubfoot) buttons. Further, unusually longdrive times are needed to upset the rivet. To counter these problems, itwas determined that a thin section 384A and 384B of the bucking dies382A and 382B, as shown in FIG. 12B, was vibrating an unacceptableamount during riveting operations. After the problem was identified,solutions were attempted using finite element analysis, data gatheringobservations, and configuration variation. As a result, it wasdetermined that a material having a density of between 14.3-14.5 G/cm³was required. Further, the material should have a compressive strengthof 650,000 psi, a minimum transverse rupture of 420,000 psi and ahardness of 72-74 Rc. Accordingly, the L-shaped bucking dies 382A and382B are preferably formed using Tungsten Carbide™ from the CarbideCorporation which meets the above requirements. More preferably, aTungsten Carbide™ grade CD-337 or ISO code G-20 or C-code C-11 is usedto form the LH and RH bucking dies 382A and 382B. Tungsten Carbide™ hastwice the density of steel and has almost twice the strength. By usingTungsten Carbide™ as the material forming the LH and RH bucking dies382A and 382B, respectively, the clinching problem was eliminated anddrive times were reduced to normal. This material could be used toimprove the riveting process any time a die must undergo torsion orother torque-induced distortion during rivet deformation, including themanual process.

Rotational Turret Subassembly:

The rotational carriage assembly of the inside end-effector 108 includesa rotational turret subassembly for rotating the LH and RH bucking bars350 and 352, respectively, along an a-axis, which rotates about the z'axis. The LH and RH bucking bars 350 and 352 are rotated and extended sothat the L-shaped bucking dies 382 and 382B, respectively, can bepositioned between the rivet shank 366 and an obstruction, such as thestringer 310, shown in FIG. 14D. Rotation of the turret subassembly ineffect moves the rivet bucking dies 382A and 382B to a pre-selectedposition (x', y') by rotating the LH and RH bucking bars 350 and 352 onthe a-axis.

The rotational turret subassembly, as shown in FIG. 12B, includes aturret bearing 386, which allows rotation of the LH and RH bucking barmodules 356 and 358, which are mounted to a rotating support 388,relative to the inside frame 354. The rotation of the rotating support385 is driven by a rotational servo-motor 390, as shown in FIG. 12A.

The position of the rotating support 388 and hence the LH and RH buckingbars 350 and 352 is monitored and reported to the control system 114 bya rotational encoder 392, as shown in FIG. 12B. When a selected one ofthe bucking bars 350 and 352 has reached its predetermined position, theCPU 398 shuts off the rotational servomotor 390 and proceeds with adrilling or fastening operation.

The inside end-effector 108 includes a plurality of pneumatic andelectrical connections 394. Preferably, these connections are quickdisconnects, allowing the easy installation and removal of the insideend-effector 108.

Control System Cart

The mini-riveter system 100 includes the control system cart 112, asshown in FIG. 15, which includes the vibratory bowl 286 for supplyingfasteners, the control system 114 including a CPU 398 and display 400.The control system cart 112 also includes an electrical power supply 402and an air/pneumatic source 404. The cart 112 is designed to transportthe inside end-effector 108 and the outside end-effector 104 to a workarea with minimal effort, and begin operations with a nominal complimentof operators. The cart 112, has the capabilities to perform all of therequired operations for fastening the lap joint 116, including processchecking/verification even before the mini-riveter system 100 is loadedonto the aircraft fuselage.

Operations:

In the first embodiment, the mini-riveter system 100 is used to fastentwo overlapping skin panels 110 forming a lap joint 116. Initially, eachof the panels 110 is cleaned and the overlapping surface of the panels110 are treated with a sealant. The panels 110 forming the lap joint 116are then temporarily fastened with deco fasteners in at least two pointsusing coordination holes as means for alignment. The panels 110 may alsobe temporarily fastened to other panels to form part of a temporarilyfastened fuselage assembly section.

Once a fuselage has been tacked together, an operator inserts index pins120 into at least three coordination holes postioning the key portion122 to protrude from the outside surface of the lap joint 116, andpositioning the reflective head 126 to protrude from the inside surfaceof the lap joint 116. External rails 102 are then positioned and alignedto the index pins 120 with the three rail ties 134A-C. Once properlyaligned, air pressure is applied via the tube portions 135A and 135B ofthe primary rail 130 and the secondary rail 132 to the vacuum generators144A-F which generate a vacuum between the panels 110 and the rails,holding them in position. The outside end-effector 104 is then liftedonto the external guide rails 102 using the primary handle 200 and thesecondary handle 202. The first and second clamshell bearing systems 204and 206 are then closed by the activation of the primary and secondaryair cylinders 212 and 214 locking the outside end-effector 104 intosliding engagement with the external guide rails 102.

The internal guide rails 106 are installed onto the inside surface ofthe panels 110 forming the lap joint 116 by positioning the upper andlower attachment brackets 308A-C and 310A-C adjacent to the frameswithin the fuselage and hooked behind the T-shaped portion of parallelstringers coupled to a respective one of the panels 110 forming the lapjoint 116. The upper and lower attachment brackets 308A-C and 310A-C arethen locked into place by tightening the levers 318A-F and 319A-Fassociated with each of the hooks 316A and 317A-F. This step roughlyensures that the internal guide rails 106 are properly aligned on the x'and y' axes on the inside surface of the lap joint 116.

Once the internal guide rails 106 have been properly installed andgenerally aligned, the inside end-effector subsystem 108 is slid ontothe ends of the internal guide rails 106 and then properly homed to thefirst of the index pins 120 using its reflecting square 128. Then, theoutside end-effector 104 is homed to the recess 125 of the key 122 of afirst of the index pins 120, thereby independently aligning both theoutside end-effector 104 and the inside end-effector 108.

The mini-riveter system 100 is directed to drill, countersink, and thenrivet a plurality of columns within the lap joint 116, where each columnconsists of three rows of rivets. First, the outside end-effector 104mini-riveter system 100 is driven from the home position or its lastknown position, to a distance along the x-axis upon which the selectedcolumn lies. Next, the pressure foot subassembly 230 is driven along they-axis to the middle row to be fastened and then is pressed against thelap joint, applying pressure of between 100 and 500 lbs. The insideend-effector 108 is driven an identical distance along its x' axis tomirror the position of the outside end-effector 104. Then, one of theLH, RH or straight bucking bars 350, 352, or 371 is extended and rotatedto an x' and y' position, such that it mirrors the position of theporthole clamp 237 of the outside end-effector 104. Further, the firstgap portion 376 of the bucking bar is positioned along the z' axis tomatch the z-axis defining the machine axis along which the drill unit262 will operate and a pressure of between 100 and 500 lbs. is exertedon the inside surface of the lap joint 116 by the bucking bar.

The external carriage 256 holding both the drill/countersink module 252and the rivet/fastener feed module 254 is moved to align the drill bitand countersink 268 along the y axis. Next the drill module 256 isactivated and moved along the z axis until a hole and countersink havingthe proper dimensions have been drilled within the lap joint 116. Afterthe drill is retracted, the external carriage 256 moves theriveter/fastener feed module 254 along the y axis into position inalignment with the newly drilled hole. The fastener feed module 254loads a selected rivet into the rivet feed fastener fingers 292A-D.Then, the inside end-effector 108 backs off the bucking bar while thefastener fingers 292A-D load the selected rivet into the newly drilledhole. The driver of the rivet module 254 is then seated against the headof the rivet, and the bucking bar is moved towards the inside surfaceuntil it contacts the shank of the rivet. The rivet is held in place bythe driver head of the pneumatic riveting unit 276. The rivet is thenupset by a series of pneumatically induced pulses from the driver headof the riveting unit 276 until it is properly seated.

One of the rivet protrusion sensors 364A and 364B compares the length ofthe rivet shaft to the length of the desired rivet to ensure that theproper rivet was loaded before allowing the driving sequence, and thenmonitors the deformation of the shank to ensure that the rivetingprocess ceases once a desired button has formed. The bucking bar and thepressure foot subassembly 230 are then released and moved to a new row.This process is repeated until each of the three rows within the columnhas been drilled, countersunk and properly riveted. Then, the inside andoutside end-effector 104 and 108 respectively are moved along the x andx' axes respectively for positioning along a new column. This process isrepeated until the entire lap joint 116 has been properly fastened.

The above-described process may be used for a plurality of mini-rivetersystems used simultaneously on different bays of an aircraft fuselage.In this embodiment, one set of operators can operate two or more systemsby setting up a second system while a first system is performing anoperation on a lap joint. In this manner production flow rates can begreatly increased without increasing manpower requirements.

FIG. 15 shows a series of program instructions coordinated by the CPU398 of the control system 114 to direct the mini-riveter system 100during positioning, drilling, and fastening operations. Flow charts fromwhich source code can be written by one skilled in the art areillustrated in FIGS. 15-17.

Referring to FIG. 15, a main routine 500, which is executed by the CPU398 begins at step 502 by requesting an input of data, including the xand y, as well as the x' and y' position of a fastener on a particularrow and column of the lap joint 116, as well as the position where thefastening process commences and the number of fasteners to be used.Next, in step 504, the CPU 398 determines whether the next position tobe fastened is that of a middle row fastener. If not, then the CPU 398proceeds to step 506 and sets a flag "middle row required first," andreturns to step 502, where it instructs the mini-riveter system 100 tomove to the next designated position. If the CPU 398 determines in step504 that the selected rivet position is a middle fastener position, itthen proceeds to step 510, where it checks if a hole has already beendrilled in that position. If a hole has been drilled, then the CPU 398proceeds to step 512, and sets a flag "no double drilling" and returnsto step 502. However, if a hole had not already been drilled, the CPU398 then proceeds to step 514 and checks whether the properdrilling/countersink module and rivet/fastener feed modules had beeninstalled. If not, the CPU 398 proceeds to step 516 and begins a holdingloop, as well as setting a flag "change modules." However, if the propermodules have been installed, then the CPU 398 proceeds to step 518 andchecks whether the outside end-effector 104 needs to be homed. If yes,the CPU 398 proceeds to step 520 and instructs the outside end-effector104 to home to the nearest of the index pin 220. If the homing step isnot required, then the CPU 398 proceeds to step 522, which invokes thehole drilling subroutine 550.

In the first step 552 of the hole drilling subroutine 550, shown in FIG.16, the CPU 398 directs the outside and inside end-effectors 104 and 108respectively to move along the x and x' axis, respectively, to theposition to be drilled. Next, in step 554, the CPU 398 moves theporthole clamp 232 of the pressure foot assembly 230 along the y axis,while the bucking bar is moved and rotated to a mirror position on they' axis. Next, in step 556, the CPU 398 directs the pressure footassembly 230 to apply a force onto the lap joint 116 for a specifieddwell time, which is selected in step 558. Then, the CPU 398 proceeds tostep 560, where it moves external the module carriage 256 to positionthe drill/countersink module 268 to the desired position along the (x,y)axes of the lap joint 116. The CPU 398 then proceeds to step 562, whereit directs the application of Boelube to the area to be drilled. Afterstep 562, the CPU 398 proceeds to step 564, where it instructs thedrilling/countersink module 268 to travel along the y axis to aspecified point for properly drilling and countersinking the hole. Then,the CPU 398 proceeds to step 566 and optionally directs the applicationof air pressure to the area to remove any drill chips. Next, the CPU 398proceeds to step 568, where it directs the inspection of the hole. TheCPU 398 then proceeds to step 570, where it ends the subroutine 550, andreturns to the main routine 500.

Once the hole drilling subroutine 550 has been completed, the CPU 398proceeds to step 524 of the main routine 500 and invokes the fasteningsubroutine 600.

In the first step 602 of the fastening subroutine 600, shown in FIG. 17,the CPU 398 directs the external module carriage 256 to position therivet driver/fastener feed module 254 to place it in alignment with thenewly drilled hole. Next, the CPU 398 proceeds to step 624 and directsthe fastener feed system to load a rivet into the assembly's fingerunits 292A-D. The CPU 398 then proceeds to step 626, where it directsthe inside end-effector assembly 108 to un-clamp the bucking bar, whichwas applying pressure to the inside surface of the lap joint 116. Instep 628, the CPU 398 backs off the bucking bar to a standby position,and the fastener feed fingers 292A-D install the rivet into the newlydrilled hole. The CPU 398 then proceeds to step 630, where it directsthe rivet head protrusion sensor to measure the length of the shaftprotruding from the inside surface of the lap joint 116. From there, theCPU 398 proceeds to step 632, where it compares the measured length ofthe shank protrusion with a tabular range of values allowable for theselected rivet to ensure that the correct rivet was loaded into thehole. If the CPU 398 determines that an improper type of rivet wasloaded into the hole or that the rivet has an abnormal shank, it thenproceeds to step 634 and sets a flag and stop further work. However, ifthe rivet is determined to be of the proper type and size, then the CPU398 proceeds to step 636 and directs the pneumatic riveter unit 276 tobegin bucking the rivet. The CPU 398 then proceeds to step 638, where itcontinues to monitor and the protrusion sensor 364A and 364B todetermine if the deformed shank has formed a proper button of aspecified height. If the button is still too large, the CPU 398 maydirect the riveting process to continue until the proper button heighthas been obtained. If the proper button height cannot be obtained afterchecking its height in step 640, the CPU 398 will proceed to step 642and set a flag and stop the system 100. However, if the CPU 398determines that the button height falls within proper tolerances, itends the subroutine and proceeds back to step 524 of the main routine500.

Once the fastening subroutine 600 has been completed, the CPU 398 of thecontrol system 114 proceeds to step 526 of the main routine 500, whereit checks to see whether another fastening operation is to occur orwhether it is the last fastener on the lap joint 116. If the CPU 398determines that the last fastener has not yet been installed, then itproceeds to step 528 and moves the mini-riveter system 100 to the nextdesired position and returns to step 502. However, if the CPU 398determines that this was the last fastener operation to occur on the lapjoint 116, then it proceeds to step 530 and displays an instruction ondisplay 400 to remove the mini-riveter system from the bays beingoperated on.

The mini-riveter system 100 is easy to set up and use, and requires onlya small amount of manpower and man hours to set up and operate. Further,the mini-riveter system 100 can fit into areas heretofore inaccessibleby drilling and fastening machines, due to its ability to be supportedand aligned by the components it is fastening and because of its smallsize. Preferably the entire mini-riveter system 100 does not exceed 200lbs., where the end-effectors are designed to weigh less than 40 lbs.and the tracks even less. Further, the mini-riveter system is small insize and was designed not to exceed an envelope of 17" along the y andy' axes by 24" along the z and z' axes. This same design concept, wherea small, light weight end-effector is supported and indexed relative tothe parts being assembled can be used in many other areas of partassembly.

Except as otherwise disclosed herein, the various components shown inoutline or block form are individually well-known and their internalconstruction and operation is not critical, either to the making or theusing of this invention.

While the detailed description above has been expressed in terms ofspecific examples, those skilled in the art will appreciate that manyother configurations could be used to accomplish the purpose of thedisclosed inventive apparatus. Accordingly, it will be appreciated thatvarious equivalent modifications of the above-described embodiments maybe made without departing from the spirit and scope of the invention.Therefore, the invention is to be limited only by the following claims.

What is claimed is:
 1. A protrusion sensor for determining theacceptability of a rivet within a component, said sensor comprising:abaseline detector which remains stationary; a movable detector whichmoves with a bucking bar module and produces a first signalproportionate to a distance between said baseline detector and saidmovable detector; a Computer Processing Unit (CPU) electronicallyconnected to said movable detector and receiving said first signal, saidCPU determining whether said rivet is acceptable by:inputting a firstdistance when said bucking bar module is clamping an inside surface ofthe component; inputting a second distance when said bucking bar moduleis seated against a shank of the rivet; subtracting the second distancefrom the first distance to determine a length of the shank protrudingfrom the inside surface of the component; and comparing the length ofthe shank against an internal table of rivet lengths to determinewhether the proper rivet was loaded into the component or whether therivet is within an acceptable tolerance.
 2. A method of detectingwhether a properly sized rivet was fed into a hole within an area of alap joint to be fastened, said method comprising the steps of:clampingthe area of the lap joint to be fastened with a bucking bar; measuring afirst distance from the end of said clamping bucking bar to a pointfixed along an axis normal to the lap joint; inserting the rivet intothe hole until a head of the rivet is flush with an outside surface ofthe lap joint and holding the rivet in this position; seating the end ofthe bucking bar against the shank of the rivet; measuring a seconddistance from the end of said seated bucking bar to said point fixedalong the axis normal to the lap joint; subtracting the second distancefrom the first distance to obtain a measured protruding shank length ofthe rivet; and comparing the measured protruding shank length against atable of rivet lengths to determine if the rivet placed in the hole insaid inserting step was the correct size of rivet required.